A properly executed baseball swing is a difficult skill to learn, because while swing mechanics can be told to a batter, the muscle coordination necessary to execute a superior swing is dauntingly complex. First, to impart optimum power the bat should be swung in an optimum swing plane that is substantially horizontal, i.e., it ideally exhibits a slight uppercut a few degrees from horizontal, although depending on ball location, other swing planes may be used.
But not only must the bat swing follow a preferred swing plane, the speed of the bat head should be at an acceptably high magnitude at a particular point in the plane, namely, the point at which contact with the ball is made. While exceptions may be made by skilled batters depending on special circumstances, e.g., in an effort to hit to the opposite field, the generally accepted optimal contact point is just in front of the batter toward the pitcher, typically where the swing plane intersects a vertical line extending from just in front of home plate.
The muscular coordination is further complicated by the fact that the head and shoulders must cooperate with the torso and hips to accelerate the bat through the contact point while maintaining the focus of the eyes on the ball at the point of contact. Allowing the shoulders to open prematurely, i.e., allowing the lead shoulder to swing toward the foul line too early in the swing, results in less power and missed pitches as the head and eyes are jerked from where focus should be, while leaving the shoulders closed too long results in less power in the swing.